1. Field of the Invention
The present invention relates to magnetic heads.
2. Description of the Related Art
With respect to magnetic heads used in video cassette recorders (VCRs), data storage equipment for computers, etc., as recording density is improved and the signal-recording mode is digitized, track width continues to decrease from year to year.
In view of these circumstances, various metal-in-gap (MIG) type magnetic heads have been used in which two magnetic core halves are bonded together by a bonding agent, such as a welding glass, with an insulating film disposed therebetween. Each magnetic core half comprises a core half formed of a ferrite or a ceramic provided with a metal magnetic film having superior soft magnetic properties.
Moreover, in recent years, for the purpose of further decreasing the track width as compared to the MIG-type magnetic heads, attempts have been made to use magnetic heads which are provided with magnetoresistive elements (MR elements) for reading magnetically recorded information. These magnetic heads have been used in VCRs, data storage equipment, etc.
FIG. 9 is a sectional view showing a principal part of a conventional magnetic head provided with an MR element, and FIG. 10 is a schematic diagram of a principal part of the magnetic head viewed from a medium-sliding surface.
In FIGS. 9 and 10, the X direction represents the track width direction of the magnetic head, the Y direction represents the travelling direction of a magnetic recording medium as well as the gap length direction of the magnetic head, and the Z direction represents a direction perpendicular to the medium-sliding surface as well as the height direction of the magnetic head. Therefore, the Y direction corresponds to a downstream direction relative to the magnetic recording medium, and a direction opposite to the Y direction corresponds to an upstream direction relative to the magnetic recording medium.
The magnetic head is a so-called xe2x80x9cmedium-sliding typexe2x80x9d magnetic head, and includes two core halves, and an MR head for reading and a write head for recording formed between the core halves.
As shown in FIGS. 9 and 10, an MR head 110 for reading is disposed on an insulating layer 104 formed on an end face 103a of a core half 103, and includes a lower shield layer 112 deposited on the insulating layer 104, a lower insulating layer 113, a magnetoresistive element (hereinafter referred to as an MR element) 120 formed on the lower insulating layer 113 and exposed to a medium-sliding surface 102, an upper insulating layer 114, and an upper shield layer 115.
The MR element 120 comprises a soft magnetic alloy thin film formed of an Nixe2x80x94Fe alloy or the like, and is connected to an MR electrode 121.
A write head 111 includes a lower core layer 115xe2x80x2 deposited on the upper shield layer 115, a gap layer 116 deposited on the lower core layer 115xe2x80x2, a thin-film coil section 117, an upper insulating layer 118 covering the thin-film coil section 117, and an upper core layer 119 connected to the gap layer 116. A base 119b of the upper core layer 119 is magnetically coupled to the lower core layer 115xe2x80x2 substantially at the center of the thin-film coil section 117.
A core-protection layer 130 composed of alumina or the like is deposited on the upper core layer 119.
As shown in FIG. 10, an insulating sliding-surface layer 131 is provided on both sides in the track width direction (in the X direction) of the MR head 110 and write head 111 and on one side in the gap length direction (the direction opposite to the Y direction) of the write head 111. The insulating sliding-surface layer 131, the MR element 120, the upper and lower shield layers 112 and 115, the upper and lower core layers 115xe2x80x2 and 119, and the gap layer 116 constitute the medium-sliding surface 102. The insulating sliding-surface layer 131 is composed of the same material as the insulating layer 104 and the upper and lower insulating layers 113 and 114, and these layers are connected and integrated.
In the MR head 110, when a sensing current supplied from the MR electrode 121 flows through the MR element 120, if a recording magnetic field from the magnetic recording medium is applied to the MR element 120, the resistance of the MR element changes, and thereby the voltage of the sensing current is changed in response to the recording magnetic field. By detecting the change in voltage, magnetically recorded information recorded in the recording medium can be read out.
Although both the upper shield layer 115 and the lower core layer 115xe2x80x2 are composed of magnetic materials, the functions of the individual layers differ from each other. Thus, the magnetic properties required are different. That is, the upper shield layer 115 must have a high magnetic permeability because it functions as a magnetic shield for the MR head 110, and the lower core layer 115xe2x80x2 must have a high magnetic flux density because it functions as a magnetic pole for the write head 111. Therefore, for example, an Ni-rich Nixe2x80x94Fe alloy is used for the upper shield layer 115 and an Fe-rich Nixe2x80x94Fe alloy is used for the lower core layer 115xe2x80x2. Since the Fe-rich Nixe2x80x94Fe alloy used for the lower core layer 115xe2x80x2 has a relatively low hardness and is therefore malleable, a plastic flow can easily occur during grinding.
However, in the conventional magnetic head, as shown in FIG. 11, when a magnetic recording medium, such as a magnetic tape, slides over the lower core layer 115xe2x80x2, a portion of the lower core layer 115xe2x80x2 may be ground and plastic flow may occur, resulting in a lingulate sag D (see the right side in FIG. 11). In some cases, so-called xe2x80x9csmearingxe2x80x9d may occur in which the lingulate sag D extends to the MR element 120, causing short-circuiting between the lower core layer 115xe2x80x2 and the MR element 120, and decreasing the reading output thereby, resulting in the magnetic head having a shortened life span.
Recently, there has also been a demand for decreasing the gap length of the MR head 110 based on the need for an improvement in magnetic recording density. Consequently, the thicknesses of the MR element 120 and the upper and lower insulating layers 114 and 113 have been decreased.
A decrease in the thickness of the upper insulating layer 114 means a decrease in the distance between the MR element 120 and the lower core layer 115xe2x80x2, and this often results in smearing.
The problem described above does not relate to so-called xe2x80x9cfloating-type magnetic recordingxe2x80x9d in which writing and reading of recorded information are performed while the magnetic head and the magnetic recording medium are moved relative to each other without making contact. However, smearing may be unavoidable when a medium-sliding-type magnetic head is employed.
It is an object of the present invention to provide a magnetic head in which smearing due to the plastic flow of the lower core layer is prevented so that the magnetic head has a longer life and is suitable for higher recording densities.
In one aspect of the present invention, a magnetic head includes an MR head and a write head which are exposed to a medium-sliding surface, wherein the MR head includes a magnetoresistive element and slides over a magnetic recording medium to read information magnetically recorded in the magnetic recording medium. The MR head further includes a shield layer provided on one side in the thickness direction of the magnetoresistive element, and a shield core layer which includes a shield section and a core section provided on the other side in the thickness direction of the magnetoresistive element, the magnetoresistive element, the shield layer, and the shield section being exposed to the medium-sliding surface. A smear-preventing layer is provided between the shield section and the core section in the shield core layer, the smear-preventing layer protruding from the medium-sliding surface farther than at least the core section. The write head includes a gap layer and a thin-film coil section deposited in that order on the shield core layer. A magnetic core layer, which is magnetically coupled to the core section, is deposited over the gap layer and the thin-film coil section so as to be insulated from the thin-film coil section, with the core section, the gap layer, and the magnetic core layer being exposed to the medium-sliding surface to form a magnetic gap.
In accordance with the magnetic head described above, even if a portion of the core section exposed to the surface facing the medium plastically flows toward the magnetoresistive element (hereinafter referred to as an MR element) due to sliding of the magnetic recording medium, the plastic flow of the core section is blocked by the smear-preventing layer provided between the shield section and the core section, and further because the smear-preventing layer protrudes from the medium-sliding surface farther than the core section. Thus avoiding a short circuit between the MR element and the core section.
In the magnetic head of the present invention, an insulating sliding-surface layer constituting the medium-sliding surface is preferably provided on the periphery of the MR head and the write head, and protrudes from the medium-sliding surface farther than the insulating sliding-surface layer.
In accordance with the magnetic head described above, since the smear-preventing layer protrudes from the medium-sliding surface farther than the insulating sliding-surface layer, the plastic flow of the core section is blocked by the smear-preventing layer, thus avoiding a short circuit between the MR element and the core section.
In the magnetic head of the present invention, the smear-preventing layer is preferably composed of a wear resistant material having a higher wear resistance to the magnetic recording medium than the wear resistance of the insulating sliding-surface layer.
In accordance with the magnetic head described above, since the smear-preventing layer is composed of a wear resistant material that has a superior wear resistance as compared to the insulating sliding-surface layer, even when the insulating sliding-surface layer wears out due to sliding of the magnetic recording medium, the smear-preventing layer does not wear, and therefore protrudes from the medium-sliding surface. Consequently, the plastic flow in the core section is blocked by the smear-preventing layer, and a short circuit between the MR element and the core section is avoided.
In another aspect of the present invention, a magnetic head includes an MR head and a write head which are exposed to a medium-sliding surface. The MR head includes a magnetoresistive element and slides over a magnetic recording medium to read information magnetically recorded in the magnetic recording medium. The MR head further includes a shield layer provided on one side in the thickness direction of the magnetoresistive element, and a shield core layer which includes a shield section and a core section provided on the other side in the thickness direction of the magnetoresistive element, the magnetoresistive element, the shield layer, and the shield section being exposed to the medium-sliding surface. A smear-preventing layer is provided between the shield section and the core section in the shield core layer. The smear-preventing layer has a higher hardness than that of at least the core section, and protrudes from the medium-sliding surface. The write head includes a gap layer and a thin-film coil section deposited in that order on the shield core layer; and a magnetic core layer, which is magnetically coupled to the core section, deposited over the gap layer and the thin-film coil section so as to be insulated from the thin-film coil section, with the core section, the gap layer, and the magnetic core layer being exposed to the medium-sliding surface to form a magnetic gap.
In accordance with the magnetic head described above, even if a portion of the core section exposed to the surface facing the medium plastically flows due to sliding of the magnetic recording medium, the plastic flow in the core section is blocked by the smear-preventing layer since the smear-preventing layer is provided between the shield section and the core section in the shield core layer and does not wear out because of its hardness. Thus, a short circuit between the MR element and the core section can be avoided.
In the magnetic head of the present invention, an insulating sliding-surface layer constituting the medium-sliding surface is preferably provided on the periphery of the MR head and the write head, and the smear-preventing layer is preferably composed of a wear resistant material having higher wear resistance to the magnetic recording medium than the wear resistance of the insulating sliding-surface layer.
Since the smear-preventing layer of the magnetic head described above is composed of a material having higher wear resistance to the magnetic recording medium than the wear resistance of the insulating sliding-surface layer, the smear-preventing layer is not worn even when the insulating sliding-surface layer is worn due to sliding of the magnetic recording medium, and only the smear-preventing layer protrudes from the medium-sliding surface. The plastic flow in the core section is thereby blocked by the smear-preventing layer, thus avoiding a short circuit between the MR element and the core section.
In the magnetic head of the present invention, the smear-preventing layer is preferably composed of SiO2. Since SiO2 is a metal oxide, and since SiO2 lacks affinity for the magnetic alloy constituting the core section, the plastically-flowing portion of the core section does not easily adhere to the smear-preventing layer, and the plastic flow in the core section is more effectively blocked by the smear-preventing layer, thereby avoiding a short circuit between the core section and the MR element. Since SiO2 has superior wear resistance to the recording medium, it is most suitable for a constituent of the smear-preventing layer.
In the magnetic head of the present invention, the insulating sliding-surface layer is preferably composed of Al2O3. Al2O3 has superior wear resistance to the magnetic recording medium in comparison with the magnetic materials constituting the MR element, the shield layer, the shield core layer, and the core layer. Therefore, the MR element, the shield layer, the shield core layer, and the core layer are more easily worn than the insulating sliding-surface layer. That is, the medium-sliding surface in the MR head and the write head is minimally worn, resulting in a very small opening between the magnetic recording medium and the medium-sliding surface, and thus writing and reading characteristics of magnetic recording can be improved.
In the magnetic head of the present invention, the shield core layer preferably includes a shield film containing the shield section and a core film containing the core section, and the shield film and the core film are connected with each other in a section in which the smear-preventing layer is not formed.
In the magnetic head of the present invention, the shield core layer preferably includes a shield film containing the shield section and a core film containing the core section, and the shield film and the core film are separated by the smear-preventing layer.
In the magnetic head of the present invention described above, the write head is preferably placed upstream in the sliding direction of the magnetic recording medium and the MR head is placed downstream.
In accordance with the magnetic head described above, since the write head is placed upstream in the sliding direction of the magnetic recording medium, the core section is placed upstream to the smear-preventing layer. Thus, even if the plastic flow in the core section extends toward the MR element, namely, to the downstream portion of the core section, the plastic flow is blocked by the smear-preventing layer, thereby avoiding a short circuit between the MR element and the core section.
Additionally, with respect to a magnetic head system in which a magnetic recording medium slides bidirectionally, when the sliding direction of the magnetic recording medium is directed from the write head to the MR head, the plastic flow in the core section is blocked by the smear-preventing layer in a manner similar to that described above.
When the sliding direction of the magnetic recording medium is directed from the MR head to the write head, a short circuit does not occur between the MR element and the core section since the plastic flow in the core section does not extend to the MR head.